1. Field of the Invention
This invention pertains to the field of ammunition and explosive devices. More particularly, this invention pertains to the field of fuzes, primers and igniting devices. In still greater particularity this invention pertains to an active optical fuze. By way of further characterization, but not by way of limitation thereto, the device pertains to an active optical, side looking fuze employing two narrow beams, which never have the surface below in their field of view. Fog and cloud discrimination circuitry is also included.
2. Description of the Prior Art
Optical fuzing systems exist in which optical beams are projected in a variety of directions. One system produces overlapping hollow conical fields around the circumference of the missile. Such an arrangement is shown in U.S. Pat. No. 3,793,958 issued to John G. Holt et al. on Feb. 26, 1974. That device employs logic circuitry requiring successively increasing amplitude return pulses to trigger the warhead. In addition,a threshold detector and an integrator are used wherein a constant false alarm rate is determined such that only signals greater than the mean value of noise signals are passed through the threshold detector. While satisfactory for its intended purpose such a device, if used in a surface directed missile, would require surface discrimination logic. In addition, the backscatter discriminator would be ineffectual in situations where the backscatter reflections were of extremely uneven character and exceeded the threshold sensitivity for detecting a minimum reflecting target.
Another optical fuzing system is shown in U.S. Pat. No. 3,786,757 issued to Irving Goldstein et al. on Jan. 23, 1974. This device uses a number of hollow beams paired such that the ordnance is triggered only if a signal is received first by one, then by the other of the pair of beams. Surface reflections would be received simultaneously and thus false triggering is rendered unlikely. While satisfactory for its intended purpose, such a device would be less useful in situations, such as fog or other aerosols, where the backscatter reflections are uneven and exceed the threshold sensitivity for detecting a minimum reflecting target.
For surface targets it would be highly desirable to have a fuze which is both unaffected by surface clutter and also has the capability to discriminate backscatter reflection such as that from fog or other aerosols. Such a device would be suitable for all weather use.
The invention operates as a pulsed optical radar employing narrow optical beams. In a roll stabilized missile the beams are never directed toward the surface below so that clutter discrimination logic is not needed. Detonation occurs when a beam intersects any target structure.
Fog and aerosol backscatter discrimination capability is incorporated into the fuze. A frequency selecting means in the form of a high-pass filter can be incorporated into the triggering circuitry as discrimination means. Another arrangement uses the time gain response of a sensitivity time control amplifier connected to the triggering circuitry and the detecting apparatus. Both discrimination devices operate at optimum efficiency for optical pulse widths of 10 milliseconds or less.